1. Field of the Invention
This invention relates to coatings for implantable devices, such as stents, containing a micronized peptide.
2. Description of the Background
Blood vessel occlusions are commonly treated by mechanically enhancing blood flow in the affected vessels, such as by employing a stent. Stents act as scaffoldings, functioning to physically hold open and, if desired, to expand the wall of the passageway. Typically stents are capable of being compressed, so that they can be inserted through small lumens via catheters, and then expanded to a larger diameter once they are at the desired location.
Stents are used not only for mechanical intervention but also as vehicles for providing biological therapy. Biological therapy can be achieved by medicating the stents. Medicated stents provide for the local administration of an active agent at the diseased site. Local delivery of an active agent is a preferred method of treatment because the agent is concentrated at a specific site and thus smaller total levels of medication can be administered in comparison to systemic dosages that often produce adverse or even toxic side effects for the patient.
One method of medicating a stent involves the use of a polymeric carrier coated onto the surface of the stent. A composition including a solvent, a polymer dissolved in the solvent, and an active agent dispersed in the blend is applied to the stent by immersing the stent in the composition or by spraying the composition onto the stent. The solvent is allowed to evaporate, leaving on the stent surfaces a coating of the polymer and the active agent impregnated in the polymer.
A potential problem with the above-described method of medicating a stent is that there can be solvent incompatibility among the components of the composition. For example, if the various components are combined to form a composition, and one of the components is immiscible in the solvent of the composition, the immiscible component will form an agglomeration. If the active agent is insoluble in the solvent used for the composition, for instance, the active agent can form crystalline masses in the wet coating and will remain clumped together in the dry coating. When the coated stent is immersed in the aqueous environment of the body, the active agent will quickly disperse into the blood stream. This result is undesirable in many circumstances because therapeutic treatment often requires a prolonged and sustained release of the active agent from the coating matrix.
In view of the foregoing, it is desirable to achieve a process that allows components with incompatible solubility profiles to be combined in a composition used to coat stents. For example, it is desirable to achieve a process that allows polycationic peptides to be combined with hydrophobic polymers. The present invention addresses such problems by providing a coating for implantable devices, and a method of making the coating.